Cicadas are well-known insects, particularly for the distinctive sounds that fill summer air. These sounds are a prominent feature of warm weather. Their activity, especially their sound production, is closely connected to the conditions of their environment.
The Optimal Temperature for Cicada Song
Cicadas exhibit their most vigorous activity and produce their loudest sounds within a specific temperature range. Cicadas begin their “singing” once temperatures rise above 22-24°C (72-75°F). For many species, the optimal temperature range for sound production is 21-32°C (70-90°F). Within this range, the intensity and frequency of their song increase as temperatures climb.
When temperatures fall below this optimal range, cicada singing diminishes. If temperatures rise excessively, beyond 31-34°C (88-93°F), cicadas may reduce their singing or seek shade to avoid heat stress. This behavior helps them manage their body temperature and conserve energy.
While the general principle of temperature dependence holds true, variations exist among the more than 3,000 cicada species. Each species may have a slightly different preferred temperature window for its acoustic displays.
The Biology Behind Temperature-Dependent Singing
Temperature’s influence on cicada sound production is deeply rooted in their biology. Cicadas are ectothermic organisms, meaning their body temperature is primarily regulated by the ambient environment. This reliance on external heat sources directly impacts their internal biological processes, including their metabolic rate and the efficiency of the specialized muscles responsible for generating sound.
Male cicadas produce sound using a pair of structures called tymbals, located on the sides of their abdomen. These tymbals are membranes with thickened ribs that rapidly buckle inward and snap back, creating a series of clicks. A large, specialized muscle, known as the tymbal muscle, controls this rapid buckling action. The clicks are amplified by an empty abdominal air sac that acts as a resonance chamber.
Optimal environmental temperatures allow the tymbal muscles to operate at peak efficiency. Higher body temperatures elevate the muscle contraction rates, which in turn permits faster oscillation of the tymbals and more robust sound production. The tymbals themselves become more flexible as temperatures rise, further facilitating sound generation.
Conversely, colder temperatures slow down metabolic processes and muscle activity, making it difficult for cicadas to produce their characteristic sounds. Excessively high temperatures can lead to overheating or muscle fatigue, which also reduces their ability to sing effectively. This temperature sensitivity ensures male cicadas perform mating calls when conditions are favorable for reproduction.